The present invention generally relates to an automotive vehicle control system and more particularly relates to techniques for determining the accuracy of a sensor output signal.
In automotive vehicle control systems which include at least two control functions, such as ABS (anti-lock system) or ABSplus and YTC (yaw torque control), it is known in the art to determine (by means of so-called tire sensors (tire wall torsion sensor or SWT)) the forces which act upon the tire during the tire rotation from the torsional deformation of the tire (depending on the position of the sensor) between a radially inward area of the tire or the hub and a radially outside area of the tire in at least one non-rotating position (WO 96/10505). At least one emitting element is provided in the side wall of the tire for this purpose according to DE 44 35 160 A1 to which is assigned at least one pick-up for measuring data that is stationarily fitted on the vehicle chassis, and a second emitter/pick-up pair for measuring data which can be configured as a conventional wheel speed sensor. In these conventional wheel speed sensors, the emitter is attached to the wheel bearing. Due to this dual pick-up arrangement, a phase change takes place between the output signals of each pick-up when the tire is deformed as a result of the forces that act upon the tire. In addition to the phase evaluation, it is also possible to evaluate the signal amplitude which provides an indication of the side wall deformation of the tire.
Further, DE 196 26 843 A1 discloses determining the rotational frequency of the tire tread by means of a tire sensor and the rotational frequency of the brake drum or brake disc by means of a conventional wheel speed sensor and evaluating the measured values individually and then comparing these results to each other. The sensors employed and their measurement results are used to determine slip in ABS or TCS functions.
In WO 97/44673, two locally offset sensors or pickups are used to measure rotational or angular movements, which reflect the torsional stress of the tire or the tire wall. The movements are in turn used to calculate the torques transmitted to the tire or the coefficient of friction experienced by the tire.
An object of the present invention is to provide an automotive vehicle control system which uses a tire sensing system in conjunction with xe2x80x98normalxe2x80x99, emitter-less tires (i.e., tires without coded side walls or magnetic areas).
The automotive vehicle control system according to the present invention includes a sensor assembly which is comprised of one (or more) pick-up(s) for measuring a tire code, and one conventional rotational speed sensor (e.g. mounted on the wheel bearing). This system permits sensing longitudinal and lateral forces on the tire and, further, the rotational speeds (as with up-to-date side wall torsion sensors (SWT)) and evaluating them for vehicle control. In this arrangement, the output signals representative of the rotational speeds, for example, the rotational frequencies of the tire sensor and the conventional wheel speed sensor known in prior art are determined and related to each other so that deviations of one signal from the other signal are detected, if necessary, in connection with further information or signals.
The automotive vehicle control system of the present invention preferably includes a tire sensor, a wheel rotational speed sensor means for examining the output signals generated by said sensors. Depending on the evaluated output signals of the sensors (or on vehicle condition variables derived therefrom), the vehicle control system automatically adapts the control logic of the automotive vehicle control system such that the YTC function is changed over to at least the ABS or ABSplus function in the presence of the only one signal which represents a wheel rotational speed or wheel rotational frequency. This ABS or ABSplus function and further secondary functions require the vehicle condition variables which are generated by the forces that act on the individual wheels and tires only for improving the function, rather than for the operability, as is the case with the YTC driving stability function.
The operability of the control logic and, thus, of the ABS or ABSplus, TCS, EBD, and EDC functions, and the YTC function can be established by using substitute signals or substitute values generated by models from the existing sensor signals based on physically different quantities, when a malfunction is detected by one of the two sensors. One such way of generating substitute values is to compare the rotational speeds of the tire sensor with those of the conventional rotational speed sensor. A malfunction detected may be due to a defect of the conventional sensor or the tire sensor, or due to tires on or in the side wall of which no magnetic areas or poles are provided which can be scanned by the pick-ups for measuring data.
To determine the sensor or pick-up for measuring data where malfunction occurs, favorably, a magnetic coding that contains scannable recordings as to whether the tire is configured as a tire sensor is favorably applied to the tire wall. It is ensured by this provision that when discrepancies between the tire signal and the conventional sensor signal are detected, the output signal of the sensor or the pick-up for measuring data can be examined which provides the signal for the wheel rotational frequency. In addition to the continuous detection which is also intended to detect the defect of the inside sensor, it is achieved that the possibly disturbed tire sensor can be identified instantaneously upon starting to drive.
In a particularly advantageous way, the comparison of the output signals of the tire sensor and the conventional sensor is effected by way of the number of their poles which are interrelated in a fixed predetermined ratio. Thus, the redundant sensor assembly made up of tire sensor and conventional sensor renders it possible with respect to the wheel rotational frequency to detect sensor faults clearly, i.e., without the assistance of plausibility criteria, and test stimuli. When deviations are found over a defined period of time, an automatic change-over to the functioning sensor takes place as well as an adaption of the control logic to the automotive vehicle control system.
The adaption of the control logic of the automotive vehicle control system (ABS, TCS, EDC, and YTC or ESP, or similar systems) which utilizes the information furnished by the sensors or pick-ups for measuring data and employed in the automotive vehicle control system is carried out automatically by way of the examined or compared wheel rotational frequencies and further information, if available. Thus, the control logic is conformed to the existing or mounted tires, (i.e. either to a normal tire or to a magnetically coded tire) because the output signals which result from the test or comparison of the rotational speeds furnished by the two sensors or pick-ups for measuring data are used to generate error and tire characteristic information, especially information relating to the presence or absence of magnetically coded tires are used on the vehicle.
Due to the fact that the control logic determines whether the output signals lie in a predetermined tolerance band and acts upon deviations only if they lie outside the tolerance band, deviations of the output signals are ignored which are based on the forces acting upon the tire that can cause displacement of the tire on the wheel rim. In addition, insignificant deviations between the output signals of the conventional sensor and the pick-up for measuring data which are not due to different wheel rotational frequencies are filtered.
Preferably, the automotive vehicle control system provides for a determination and/or compensation of the shift of the phase marks or the poles between the tire sensor and the one conventional sensor during predetermined driving conditions by means which are effective for correcting the displacement of the tire on the rim. The phase position is e.g. determined by a learning method which is measured during constant stable driving or at constant driving speed of the vehicle. Because the side wall deformation is reproduced as a result of the forces which are produced by positive or negative acceleration of the wheel, and these quantities are thus in a fixed interrelationship, it is possible to correlate the acceleration measured by a sensor to the phase shift and, thus, compensate a possibly occurring fault. Further, the derivative of the phase signal can be made use of in the event of abrupt changes.
A distinction can be made between the following strategies for the driving conditions:
1. driving at constant speed without acceleration or deceleration
2. accelerated driving
3. accelerated driving with TCS intervention (TCS Traction Slip Control system)
4. decelerated driving
5. decelerated driving with ABS intervention (ABS anti-lock system)
6. ESP intervention (Electronic Stability Program).
The phase shift of the two sensor signals is sensed and stored at constant speeds. This determines a basic offset which can be updated at constant driving. When deviations of the phase shift between the two sensor signals, i.e., the signals of the wheel sensor and the tire sensor, are detected at positive or negative acceleration, and the said deviations lie above a predetermined threshold value or outside a tolerance band, a relative movement between the tire and the rim is assumed which can be corrected by means of correction factors or in dependence on the phase shifts sensed at the xe2x80x98otherxe2x80x99 wheels. In a traction slip or ESP intervention, the coefficient of friction is determined in addition, the influence of which on the sensing of the relative movement between tire and rim must be separated in the driving conditions 3, 5, and 6. The coefficient of friction can be determined by way of the brake characteristic (for example, surface of the brake piston, number of pistons per wheel brake, coefficient of friction between disc and brake lining, and similar factors) and by way of the brake pressure calculated on the basis of a pressure model.